This invention relates to the field of surgical devices used primarily for the repair or replacement of human tissue, including, but not limited to, the nucleus pulposus of the spine. The invention further relates to the method of using such devices.
The spinal column is a flexible chain of closely linked vertebral bodies. In a normal human spine there are seven cervical, twelve thoracic and five lumbar vertebral bodies. Below the lumbar vertebrae are the sacrum and coccyx. Each individual vertebra has an outer shell of hard, dense bone. Inside the vertebra is a honeycomb of cancellous bone containing red bone marrow. All of the red blood cells and many of the white blood cells are generated inside this cancellous bone, where the blood cells mature before being released into the blood circulation.
The spinal disc serves as a cushion between the vertebral bodies to permit controlled motion. A healthy disc consists of three components: a gelatinous inner core called the nucleus pulposus; a series of overlapping and laminated plies of tough fibrous rings called the annulus fibrosus; and two superior and inferior thin cartilage layers, connecting the disc to the thin cortical bone of the vertebral bodies, called the endplates.
The spinal disc may be displaced or damaged due to trauma or disease, such as a herniation or degenerative disc disease.
A herniated disc may bulge out and compress itself onto a nerve, resulting in lower leg pain, loss of muscle control, or paralysis. To treat a herniated disc, the offending nucleus portions are generally removed surgically.
Disc degeneration gradually reduces disc height, forcing the annulus to buckle, tear or separate radially or circumferentially, and causing persistent and disabling back pain. Degenerative disc disease is generally treated presently by surgically removing the nucleus and fusing the adjacent vertebral bodies to stabilize the joint.
In either case, whether removing a portion of the nucleus or all of the nucleus, these procedures ultimately place greater stress on adjacent discs to compensate for the lack of motion, which may cause premature degeneration of those adjacent discs.
Modern trends in surgery include the restoration of bodily function and form (i.e., repair) of anatomical structures through the use of minimally invasive surgical techniques. The ability to surgically repair damaged tissues or joints, creating as few and as small incisions as possible, produces less trauma, less pain and better clinical outcomes in general.
An emerging technique to treat degenerative disc disease is to replace the degenerated nucleus with a prosthetic nucleus in an attempt to restore function, versus fusion which severely limits the function of the spine. Since a degenerated nucleus can be removed using relatively small diameter instruments (e.g. 5 mm or less), this approach is more conducive to minimally invasive techniques.
A deficiency of current minimally invasive surgical techniques to replace the nucleus is the difficulty in determining whether enough space in the disc has been created to properly fit an implant. Creating the proper dimension cavity may be particularly important when implanting a device that expands, such as with a hydrogel implant. If the cavity created is larger than the implant, unintended implant movement or instability can occur. If the cavity created is smaller than the implant, an implant either may not fit, may not be positioned correctly or an expandable device may not achieve its proper functional shape.
It is, therefore, one object of the present invention to provide a device and method for determining how much space is created in human tissue, particularly when the space is in a visually impaired location.
A further object of the invention is to provide a device and method for determining how much space is created in the inner portion of the intervertebral disc space to facilitate the implantation of an artificial nucleus pulposus. The present invention is adapted to be placed through a small opening created in the annulus to minimize trauma to surrounding tissue.
With the above and other objects in view, a feature of the invention is the provision of a device for determining parameters of a blind void. The device comprises an elongated rigid rod, and an actuator extending lengthwise of the rod and slidably movable relative to the rod, the actuator having a distal end for insertion into the void. A first flexible element is fixed at one end thereof to the rod proximate the distal end of the rod. A second flexible element is fixed at one end thereof to the rod and proximally removed from the distal end of the rod and from the first element. Movement of the actuator is operative to cause equal movements of the distal end portions of the first and second elements, to cause the first element to bulge outwardly from the rod to engage interior walls of the void and to cause the second element to bulge outwardly in a configuration substantially duplicative of the first element bulge, the second element being outside of the void and subject to observation.
In accordance with a further feature of the invention, there is provided a method for determining parameters of a blind void, the method comprising the steps of providing a device comprising an elongated rigid rod, a first flexible element fixed at one end thereof to the rod proximate a distal end of the rod, a second flexible element fixed at one end thereof to the rod and proximally removed from the distal end of the rod and from the first element, and an actuator extending lengthwise of the rod and engageable with distal end portions of the first and second elements. The method further includes the steps of inserting the distal end of the actuator and the first element into the void, moving the actuator to cause movements of the distal end portions of the first and second elements, to cause the first element to bulge outwardly to engage interior walls of the void, and to cause the second element to bulge outwardly in a configuration duplicative of the first element bulge, the second element being outside of the void, and determining from the size of the second element the size of the first element and thereby the void.
The above and other features of the invention, including various novel details of construction and combinations of parts and method steps, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular device and method embodying the invention are described by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.